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Meir A, Macé K, Vegunta Y, Williams SM, Waksman G. Substrate recruitment mechanism by gram-negative type III, IV, and VI bacterial injectisomes. Trends Microbiol 2023; 31:916-932. [PMID: 37085348 DOI: 10.1016/j.tim.2023.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 03/09/2023] [Accepted: 03/13/2023] [Indexed: 04/23/2023]
Abstract
Bacteria use a wide arsenal of macromolecular substrates (DNA and proteins) to interact with or infect prokaryotic and eukaryotic cells. To do so, they utilize substrate-injecting secretion systems or injectisomes. However, prior to secretion, substrates must be recruited to specialized recruitment platforms and then handed over to the secretion apparatus for secretion. In this review, we provide an update on recent advances in substrate recruitment and delivery by gram-negative bacterial recruitment platforms associated with Type III, IV, and VI secretion systems.
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Affiliation(s)
- Amit Meir
- Institute of Structural and Molecular Biology, Birkbeck and UCL, Malet Street, London WC1E 7HX, UK; Current address: MRC Centre for Virus Research, School of Infection and Immunity, University of Glasgow, Glasgow, UK.
| | - Kévin Macé
- Institute of Structural and Molecular Biology, Birkbeck and UCL, Malet Street, London WC1E 7HX, UK
| | - Yogesh Vegunta
- Institute of Structural and Molecular Biology, Birkbeck and UCL, Malet Street, London WC1E 7HX, UK
| | - Sunanda M Williams
- Institute of Structural and Molecular Biology, Birkbeck and UCL, Malet Street, London WC1E 7HX, UK
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, Birkbeck and UCL, Malet Street, London WC1E 7HX, UK; Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK.
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Navarrete KM, Bumba L, Prudnikova T, Malcova I, Allsop TR, Sebo P, Kamanova J. BopN is a Gatekeeper of the Bordetella Type III Secretion System. Microbiol Spectr 2023; 11:e0411222. [PMID: 37036369 PMCID: PMC10269732 DOI: 10.1128/spectrum.04112-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Accepted: 03/17/2023] [Indexed: 04/11/2023] Open
Abstract
The classical Bordetella species infect the respiratory tract of mammals. While B. bronchiseptica causes rather chronic respiratory infections in a variety of mammals, the human-adapted species B. pertussis and B. parapertussisHU cause an acute respiratory disease known as whooping cough or pertussis. The virulence factors include a type III secretion system (T3SS) that translocates effectors BteA and BopN into host cells. However, the regulatory mechanisms underlying the secretion and translocation activity of T3SS in bordetellae are largely unknown. We have solved the crystal structure of BopN of B. pertussis and show that it is similar to the structures of gatekeepers that control access to the T3SS channel from the bacterial cytoplasm. We further found that BopN accumulates at the cell periphery at physiological concentrations of calcium ions (2 mM) that inhibit the secretion of BteA and BopN. Deletion of the bopN gene in B. bronchiseptica increased secretion of the BteA effector into calcium-rich medium but had no effect on secretion of the T3SS translocon components BopD and BopB. Moreover, the ΔbopN mutant secreted approximately 10-fold higher amounts of BteA into the medium of infected cells than the wild-type bacteria, but it translocated lower amounts of BteA into the host cell cytoplasm. These data demonstrate that BopN is a Bordetella T3SS gatekeeper required for regulated and targeted translocation of the BteA effector through the T3SS injectisome into host cells. IMPORTANCE The T3SS is utilized by many Gram-negative bacteria to deliver effector proteins from bacterial cytosol directly into infected host cell cytoplasm in a regulated and targeted manner. Pathogenic bordetellae use the T3SS to inject the BteA and BopN proteins into infected cells and upregulate the production of the anti-inflammatory cytokine interleukin-10 (IL-10) to evade host immunity. Previous studies proposed that BopN acted as an effector in host cells. In this study, we report that BopN is a T3SS gatekeeper that regulates the secretion and translocation activity of Bordetella T3SS.
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Affiliation(s)
- Kevin Munoz Navarrete
- Laboratory of Infection Biology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Ladislav Bumba
- Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Tatyana Prudnikova
- Faculty of Science, University of South Bohemia in Ceske Budejovice, Ceske Budejovice, Czech Republic
| | - Ivana Malcova
- Laboratory of Infection Biology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Tania Romero Allsop
- Laboratory of Infection Biology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Peter Sebo
- Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Jana Kamanova
- Laboratory of Infection Biology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic
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CesL Regulates Type III Secretion Substrate Specificity of the Enteropathogenic E. coli Injectisome. Microorganisms 2021; 9:microorganisms9051047. [PMID: 34067942 PMCID: PMC8152094 DOI: 10.3390/microorganisms9051047] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 04/27/2021] [Accepted: 04/27/2021] [Indexed: 11/23/2022] Open
Abstract
The type III secretion system (T3SS) is a complex molecular device used by several pathogenic bacteria to translocate effector proteins directly into eukaryotic host cells. One remarkable feature of the T3SS is its ability to secrete different categories of proteins in a hierarchical manner, to ensure proper assembly and timely delivery of effectors into target cells. In enteropathogenic Escherichia coli, the substrate specificity switch from translocator to effector secretion is regulated by a gatekeeper complex composed of SepL, SepD, and CesL proteins. Here, we report a characterization of the CesL protein using biochemical and genetic approaches. We investigated discrepancies in the phenotype among different cesL deletion mutants and showed that CesL is indeed essential for translocator secretion and to prevent premature effector secretion. We also demonstrated that CesL engages in pairwise interactions with both SepL and SepD. Furthermore, while association of SepL to the membrane does not depended on CesL, the absence of any of the proteins forming the heterotrimeric complex compromised the intracellular stability of each component. In addition, we found that CesL interacts with the cytoplasmic domains of the export gate components EscU and EscV. We propose a mechanism for substrate secretion regulation governed by the SepL/SepD/CesL complex.
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Schureck MA, Darling JE, Merk A, Shao J, Daggupati G, Srinivasan P, Olinares PDB, Rout MP, Chait BT, Wollenberg K, Subramaniam S, Desai SA. Malaria parasites use a soluble RhopH complex for erythrocyte invasion and an integral form for nutrient uptake. eLife 2021; 10:e65282. [PMID: 33393463 PMCID: PMC7840181 DOI: 10.7554/elife.65282] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Accepted: 01/04/2021] [Indexed: 12/12/2022] Open
Abstract
Malaria parasites use the RhopH complex for erythrocyte invasion and channel-mediated nutrient uptake. As the member proteins are unique to Plasmodium spp., how they interact and traffic through subcellular sites to serve these essential functions is unknown. We show that RhopH is synthesized as a soluble complex of CLAG3, RhopH2, and RhopH3 with 1:1:1 stoichiometry. After transfer to a new host cell, the complex crosses a vacuolar membrane surrounding the intracellular parasite and becomes integral to the erythrocyte membrane through a PTEX translocon-dependent process. We present a 2.9 Å single-particle cryo-electron microscopy structure of the trafficking complex, revealing that CLAG3 interacts with the other subunits over large surface areas. This soluble complex is tightly assembled with extensive disulfide bonding and predicted transmembrane helices shielded. We propose a large protein complex stabilized for trafficking but poised for host membrane insertion through large-scale rearrangements, paralleling smaller two-state pore-forming proteins in other organisms.
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Affiliation(s)
- Marc A Schureck
- Laboratory of Malaria and Vector Research, NIAID, National Institutes of HealthRockvilleUnited States
| | - Joseph E Darling
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of HealthBethesdaUnited States
| | - Alan Merk
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of HealthBethesdaUnited States
| | - Jinfeng Shao
- Laboratory of Malaria and Vector Research, NIAID, National Institutes of HealthRockvilleUnited States
| | - Geervani Daggupati
- Department of Molecular Microbiology and Immunology, and Johns Hopkins Malaria Institute, Johns Hopkins Bloomberg School of Public HealthBaltimoreUnited States
| | - Prakash Srinivasan
- Department of Molecular Microbiology and Immunology, and Johns Hopkins Malaria Institute, Johns Hopkins Bloomberg School of Public HealthBaltimoreUnited States
| | - Paul Dominic B Olinares
- Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller UniversityNew YorkUnited States
| | - Michael P Rout
- Laboratory of Cellular and Structural Biology, The Rockefeller UniversityNew YorkUnited States
| | - Brian T Chait
- Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller UniversityNew YorkUnited States
| | - Kurt Wollenberg
- Office of Cyber Infrastructure & Computational Biology, National Institute of Allergy and Infectious Diseases, National Institutes of HealthBethesdaUnited States
| | - Sriram Subramaniam
- Department of Biochemistry and Molecular Biology, University of British ColumbiaVancouverCanada
| | - Sanjay A Desai
- Laboratory of Malaria and Vector Research, NIAID, National Institutes of HealthRockvilleUnited States
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A Reporter System for Fast Quantitative Monitoring of Type 3 Protein Secretion in Enteropathogenic E. coli. Microorganisms 2020; 8:microorganisms8111786. [PMID: 33202599 PMCID: PMC7696366 DOI: 10.3390/microorganisms8111786] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 11/06/2020] [Accepted: 11/09/2020] [Indexed: 12/16/2022] Open
Abstract
The type 3 secretion system is essential for pathogenesis of several human and animal Gram-negative bacterial pathogens. The T3SS comprises a transmembrane injectisome, providing a conduit from the bacterial cytoplasm to the host cell cytoplasm for the direct delivery of effectors (including toxins). Functional studies of T3SS commonly monitor the extracellular secretion of proteins by SDS-PAGE and western blot analysis, which are slow and semi-quantitative in nature. Here, we describe an enzymatic reporter-based quantitative and rapid in vivo assay for T3SS secretion studies in enteropathogenic E. coli (EPEC). The assay monitors the secretion of the fusion protein SctA-PhoA through the injectisome based on a colorimetric assay that quantifies the activity of alkaline phosphatase. We validated the usage of this reporter system by following the secretion in the absence of various injectisome components, including domains of the gatekeeper essential for T3SS function. This platform can now be used for the isolation of mutations, functional analysis and anti-virulence compound screening.
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Lyons BJE, Strynadka NCJ. On the road to structure-based development of anti-virulence therapeutics targeting the type III secretion system injectisome. MEDCHEMCOMM 2019; 10:1273-1289. [PMID: 31534650 PMCID: PMC6748289 DOI: 10.1039/c9md00146h] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 06/07/2019] [Indexed: 12/19/2022]
Abstract
The type III secretion system injectisome is a syringe-like multimembrane spanning nanomachine that is essential to the pathogenicity but not viability of many clinically relevant Gram-negative bacteria, such as enteropathogenic Escherichia coli, Salmonella enterica and Pseudomonas aeruginosa. Due to the rise in antibiotic resistance, new strategies must be developed to treat the growing spectre of drug resistant infections. Targeting the injectisome via an 'anti-virulence strategy' is a promising avenue to pursue as an alternative to the more commonly used bactericidal therapeutics, which have a high propensity for resulting resistance development and often more broad killing profile, including unwanted side effects in eliminating favourable members of the microbiome. Building on more than a decade of crystallographic work of truncated or isolated forms of the more than two dozen components of the secretion apparatus, recent advances in the field of single-particle cryo-electron microscopy have allowed for the elucidation of atomic resolution structures for many of the type III secretion system components in their assembled, oligomerized state including the needle complex, export apparatus and ATPase. Cryo-electron tomography studies have also advanced our understanding of the direct pathogen-host interaction between the type III secretion system translocon and host cell membrane. These new structural works that further our understanding of the myriad of protein-protein interactions that promote injectisome function will be highlighted in this review, with a focus on those that yield promise for future anti-virulence drug discovery and design. Recently developed inhibitors, including both synthetic, natural product and peptide inhibitors, as well as promising new developments of immunotherapeutics will be discussed. As our understanding of this intricate molecular machinery advances, the development of anti-virulence inhibitors can be enhanced through structure-guided drug design.
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Affiliation(s)
- Bronwyn J E Lyons
- Department of Biochemistry and Molecular Biology and Center for Blood Research , University of British Columbia , 2350 Health Sciences Mall , Vancouver , British Columbia V6T 1Z3 , Canada .
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology and Center for Blood Research , University of British Columbia , 2350 Health Sciences Mall , Vancouver , British Columbia V6T 1Z3 , Canada .
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Portaliou AG, Tsolis KC, Loos MS, Balabanidou V, Rayo J, Tsirigotaki A, Crepin VF, Frankel G, Kalodimos CG, Karamanou S, Economou A. Hierarchical protein targeting and secretion is controlled by an affinity switch in the type III secretion system of enteropathogenic Escherichia coli. EMBO J 2017; 36:3517-3531. [PMID: 29109154 DOI: 10.15252/embj.201797515] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Revised: 09/05/2017] [Accepted: 10/11/2017] [Indexed: 11/09/2022] Open
Abstract
Type III secretion (T3S), a protein export pathway common to Gram-negative pathogens, comprises a trans-envelope syringe, the injectisome, with a cytoplasm-facing translocase channel. Exported substrates are chaperone-delivered to the translocase, EscV in enteropathogenic Escherichia coli, and cross it in strict hierarchical manner, for example, first "translocators", then "effectors". We dissected T3S substrate targeting and hierarchical switching by reconstituting them in vitro using inverted inner membrane vesicles. EscV recruits and conformationally activates the tightly membrane-associated pseudo-effector SepL and its chaperone SepD. This renders SepL a high-affinity receptor for translocator/chaperone pairs, recognizing specific chaperone signals. In a second, SepD-coupled step, translocators docked on SepL become secreted. During translocator secretion, SepL/SepD suppress effector/chaperone binding to EscV and prevent premature effector secretion. Disengagement of the SepL/SepD switch directs EscV to dedicated effector export. These findings advance molecular understanding of T3S and reveal a novel mechanism for hierarchical trafficking regulation in protein secretion channels.
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Affiliation(s)
- Athina G Portaliou
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Konstantinos C Tsolis
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Maria S Loos
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Vassileia Balabanidou
- Institute of Molecular Biology and Biotechnology, FORTH (Foundation of Research and Technology), University of Crete, Heraklion, Greece
| | - Josep Rayo
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Alexandra Tsirigotaki
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Valerie F Crepin
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | - Gad Frankel
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | | | - Spyridoula Karamanou
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Anastassios Economou
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
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Regulation of Type III Secretion of Translocon and Effector Proteins by the EsaB/EsaL/EsaM Complex in Edwardsiella tarda. Infect Immun 2017. [PMID: 28630070 DOI: 10.1128/iai.00322-17] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The type III secretion system (T3SS) plays a crucial role in the pathogenesis of many Gram-negative bacteria, including Edwardsiella tarda, an important fish pathogen. Within the E. tarda T3SS, there are three proteins (EsaB/EsaL/EsaM) that are homologous to proteins present in many other bacteria, including SpiC/SsaL/SsaM in Salmonella, SepD/SepL/CesL in enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC), and YscB/YopN/SycN in Yersinia EsaL was found to interact with both EsaB and EsaM within the bacterial cell, as revealed by a coimmunoprecipitation assay. Moreover, EsaM is required for EsaB stability, and the two proteins interact with each other. EsaB, EsaL, and EsaM are all indispensable for the secretion of the T3SS translocon protein EseC into supernatants under pH 5.5 and pH 7.2 conditions. Unlike EseC, EseG is a T3SS effector whose secretion is suppressed by EsaL at pH 7.2 while it is promoted at pH 5.5 condition. Despite this finding, mutant strains lacking EsaB, EsaL, or EsaM (i.e., the ΔesaB, ΔesaL, or ΔesaM strain, respectively) were all outcompeted by wild-type E. tarda during a coinfection model. These results demonstrate that EsaB/EsaL/EsaM form a ternary complex controlling the secretion of T3SS translocon and effector proteins and contributing to E. tarda pathogenesis.
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Roehrich AD, Bordignon E, Mode S, Shen DK, Liu X, Pain M, Murillo I, Martinez-Argudo I, Sessions RB, Blocker AJ. Steps for Shigella Gatekeeper Protein MxiC Function in Hierarchical Type III Secretion Regulation. J Biol Chem 2016; 292:1705-1723. [PMID: 27974466 PMCID: PMC5290946 DOI: 10.1074/jbc.m116.746826] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 12/14/2016] [Indexed: 01/18/2023] Open
Abstract
Type III secretion systems are complex nanomachines used for injection of proteins from Gram-negative bacteria into eukaryotic cells. Although they are assembled when the environmental conditions are appropriate, they only start secreting upon contact with a host cell. Secretion is hierarchical. First, the pore-forming translocators are released. Second, effector proteins are injected. Hierarchy between these protein classes is mediated by a conserved gatekeeper protein, MxiC, in Shigella. As its molecular mechanism of action is still poorly understood, we used its structure to guide site-directed mutagenesis and to dissect its function. We identified mutants predominantly affecting all known features of MxiC regulation as follows: secretion of translocators, MxiC and/or effectors. Using molecular genetics, we then mapped at which point in the regulatory cascade the mutants were affected. Analysis of some of these mutants led us to a set of electron paramagnetic resonance experiments that provide evidence that MxiC interacts directly with IpaD. We suggest how this interaction regulates a switch in its conformation that is key to its functions.
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Affiliation(s)
- A Dorothea Roehrich
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Enrica Bordignon
- the Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Selma Mode
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Da-Kang Shen
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Xia Liu
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Maria Pain
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Isabel Murillo
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Isabel Martinez-Argudo
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom; the Área de Genética, Facultad de Ciencias Ambientales y Bioquímica, Universidad de Castilla-La Mancha, E-45071 Toledo, Spain
| | - Richard B Sessions
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Ariel J Blocker
- From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
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Gaytán MO, Martínez-Santos VI, Soto E, González-Pedrajo B. Type Three Secretion System in Attaching and Effacing Pathogens. Front Cell Infect Microbiol 2016; 6:129. [PMID: 27818950 PMCID: PMC5073101 DOI: 10.3389/fcimb.2016.00129] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 09/27/2016] [Indexed: 02/06/2023] Open
Abstract
Enteropathogenic Escherichia coli and enterohemorrhagic E. coli are diarrheagenic bacterial human pathogens that cause severe gastroenteritis. These enteric pathotypes, together with the mouse pathogen Citrobacter rodentium, belong to the family of attaching and effacing pathogens that form a distinctive histological lesion in the intestinal epithelium. The virulence of these bacteria depends on a type III secretion system (T3SS), which mediates the translocation of effector proteins from the bacterial cytosol into the infected cells. The core architecture of the T3SS consists of a multi-ring basal body embedded in the bacterial membranes, a periplasmic inner rod, a transmembrane export apparatus in the inner membrane, and cytosolic components including an ATPase complex and the C-ring. In addition, two distinct hollow appendages are assembled on the extracellular face of the basal body creating a channel for protein secretion: an approximately 23 nm needle, and a filament that extends up to 600 nm. This filamentous structure allows these pathogens to get through the host cells mucus barrier. Upon contact with the target cell, a translocation pore is assembled in the host membrane through which the effector proteins are injected. Assembly of the T3SS is strictly regulated to ensure proper timing of substrate secretion. The different type III substrates coexist in the bacterial cytoplasm, and their hierarchical secretion is determined by specialized chaperones in coordination with two molecular switches and the so-called sorting platform. In this review, we present recent advances in the understanding of the T3SS in attaching and effacing pathogens.
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Affiliation(s)
- Meztlli O Gaytán
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Verónica I Martínez-Santos
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Eduardo Soto
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Bertha González-Pedrajo
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
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